Controlling a high speed asynchronous motor in a weaving machine

ABSTRACT

A drive device for a weaving machine has a motor control unit connected to an asynchronous motor. An electric supply network supplies the motor control unit with electric power which the motor control unit converts to have a substantially higher frequency. This higher frequency power is then supplied to the asynchronous motor causing the motor to operate at a high r.p.m. A speed reducing unit is connected between the motor and a drive shaft of the weaving machine. The speed reducing unit reduces the r.p.m. of the motor and the motor drives the weaving machine via the drive shaft at the r.p.m. of the weaving machine.

FIELD OF THE INVENTION

The present invention relates to a drive device in a weaving machinecomprising an asynchronous motor which can be powered from an electricpower supply network operating at conventional frequency, e.g. afrequency of 50 or 60 Hz, for example. The asynchronous motor exhibits,or is connected to, a motor control and drives a drive unit/drive shaftin the weaving machine via a speed-reducing unit.

The invention also relates to a device for increasing the efficiency ina weaving machine system comprising one or more weaving machines and inwhich a respective weaving machine can be driven by an asynchronousmotor which can be powered from an electric power supply network. Theinvention also relates to a device in a weaving machine which can bedriven by means of an asynchronous motor which in a drive system,actuates the drive unit/drive shaft of the weaving machine via aspeed-reducing apparatus and in which at least one flywheel is arrangedto smooth peaks of torque caused by the fact that the weaving machine,during the weaving cycle, has a varying torque requirement. Finally, theinvention relates also to a device in a weaving machine which can bedriven by means of an asynchronous motor which actuates the driveunit/drive shaft of the weaving machine via a speed-reducing apparatusand in which a computer apparatus is arranged to predict optimal weavingmachine speed for a respective yarn character. By yarn character is heremeant quality, thickness, etc.

Regarding the types of weaving machines in which the invention can beused, weaving machines of the "Air Jet", "Water Jet" type, gripperweaving machines, projectile weaving machines, etc. can be mentioned.

It is previously known to use an asynchronous motor to drive a weavingmachine of the type in question. The motor size for the particular typesof weaving machines can be within the range of about 3-6 kW and canoperate at a rotation speed of between 1400 and 2800 r.p.m., i.e. 2 and4-pole asynchronous motors are utilized. The rotation speed of theweaving machine can lie in the range 500-1200 r.p.m., which means thatthe drive apparatus in question comprises a speed-reducing unit betweenthe asynchronous motor and the drive member/drive shaft of the weavingmachine.

The rotation speed of the weaving machine is dependent, among otherthings, upon the mechanical strength of the yarn in question. Higherspeeds of the weaving machine produce higher load on the yarn and viceversa. Changes to the speed of the weaving machine have thus generallyinvolved altering the setting of the speed-reducing apparatus (e.g. by achange of wheel in the gearbox and by similar techniques).

It is also known, in connection with weaving machines and their utilizedasynchronous motors, to make use of a motor control/motor controls. Thisusage has hitherto involved adjusting the existing rotation speed of theasynchronous motor downwards in relation to its normal operating speed.If, for example, the motor is designed to operate at the rotationalspeed of 2800 r.p.m., a downward adjustment has been made from arotation speed close to this to a lower rotational speed, e.g. to arotational speed of 2000 r.p.m. or higher. It is possible per se toadjust the rotational speed of a standard motor upwardly, but with thedisadvantage that the torque falls in proportion to the rotational speedincrease. Power losses have thereby been generated and the motor controlas such has been regarded, moreover, as a purely additional auxiliaryapparatus which gave rise to an additional investment cost. The abovedisadvantages have hitherto had to be offset by higher productivity orby lower profits.

The object of the invention is to propose a device which solves, amongother things, these problems. The invention makes it possible, moreover,to use a smaller motor of substantially lower (e.g. 50% lower) weight.This, together with the increased efficiency, means that the motorcontrol as such pays for itself within a relatively short (e.g. 6-month)running or usage period. it is essential to be able to run therespective weaving machine at optimal speed with regard to yarn type andyarn quality. It is therefore important that the asynchronous motor beable to operate with small variations above the optimal motor rotation.It is thereby possible to approach the optimal limit for the weavingspeed, since there is no need to risk peaks of speed beyond the strengthof the yarn due to uncontrollable speed variations/speeds. The inventionsolves this problem.

In order to achieve a good and even weaving quality, it is essential toobtain a certain or desired quantity of stored kinetic energy in thesystem, which is achieved by the invention. It is essential thatoptimally stored energy should be able to be acquired. Inadequately lowkinetic energy produces rotation speed variations and excessively highkinetic energy produces long start times. Likewise, it is important thatthe dimensions and weights of components forming part of the weavingmachine be reduced. This is also achieved by the invention, whichenables the sizes and weights of the flywheel or corresponding sizes andweights to be substantially reduced.

Especially where weaving machines are run in two or three shifts, it isessential to increase the efficiency throughout the system. The need,for example, to use a large number of motor types and/or make a largenumber of voltage adjustments by means of transformers also have to bereduced. The invention solves this problem and proposes, for example,that the motor control provides the particular motor with a correctvoltage irrespective of large differences in the supply voltage (linevoltage). It is also essential that the mass moment of inertia should bekept at an optimal level and hence prevent the occurrence of large timedelays upon stopping and starting of the weaving machines or rotationspeed variations due to inadequate kinetic energy. This too is solved bythe invention. There is also a general trend that the weaving machineshould become more user-friendly and that, for example, manual settingfunctions can be substantially reduced. The invention solves thisproblem.

What can primarily be deemed to be characteristic of a drive deviceintended for a weaving machine is that the motor control is arranged toconvert the frequency of the electricity network to a substantiallyhigher frequency and hence procure for the asynchronous motor asubstantially higher rotation speed compared with a case in which acorresponding conventional asynchronous motor is driven at the frequencyof the electricity network and that the speed-reducing unit is arrangedto reduce the substantially higher rotation speed to the (optimal)running speed of the weaving machine.

A device for increasing the efficiency in a weaving machine system is tobe characterized by the fact that the respective asynchronous motor isconnected to the power-supply network via frequency-increasing memberswhich, to the asynchronous motor, produce a frequency whichsubstantially exceeds the frequency of the network in order to obtain amarked overspeeding of the asynchronous motor and that the latter isassigned an electronic compensation member which stabilizes the inputvoltage of the asynchronous motor.

What can primarily be deemed to be characteristic of a device in aweaving machine in which at least one flywheel is arranged to smoothpeaks of torque can primarily be deemed to be characterized by the factthat the asynchronous motor operates at a substantially oversped stateand that the flywheel(s) is/are arranged in connection with thehigh-speed side of the drive system in order, on this, to procurestorage of the most substantial part of generated kinetic energy withinthe system.

What can primarily be deemed to be characteristic of a device in aweaving machine in which a computer apparatus, using the faultstatistics of the weaving machine as input data, is arranged to predictan optimal weaving machine speed for a respective yarn character is thatthe asynchronous motor can be fed via a frequency-increasing unit whichsubstantially overspeeds the motor and that the frequency-increasingunit is controllable from the computer apparatus in order to relate thefrequency increase, and hence the rotation speed of the motor, to theoptimal-weaving machine speed.

The invention serves to indicate a new way of using a motor controlfunction, which, instead of conventional downward adjustment of therotation speed, is arranged to produce a substantial upward adjustmentof the rotational speed. It also becomes possible, by virtue of theinvention, to indicate means of adapting other components which are runjointly with the oversped asynchronous motor within the total drivesystem for the weaving machine.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention is to be described below, reference herein beingmade to the appended drawings, in which:

FIG. 1 shows the basic structure of a drive system for a weavingmachine, comprising a computer apparatus for the control of the weavingmachine, and

FIG. 2 shows, in block diagram form, an illustrative embodiment of themotor control function.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

In FIG. 1, a weaving machine is symbolized by 1. A weave produced withthe weaving machine is indicated by 2 and warp threads by 3 and weftthreads or weft yarn by 4. The weaving machine comprises a driveshaft/main drive shaft 5.

According to the invention, the drive shaft 5 can be driven by anasynchronous motor 6 which is provided with an output drive shaft 7. Thedriving of the drive shaft 5 of the weaving machine is effected via aspeed-reducing apparatus 8, which in the illustrative embodimentcomprises a drive belt 9. The shaft 7 is provided with a belt pulley 10and the transmission to the drive shaft 5 of the weaving machine iseffected by means of belt pulley 11. The diameters of the belt pulleys10 and 11 determine the reduction of the rotational speed of thesynchronous motor 6 to a rotational speed of the shaft 5 which isappropriate for the weaving machine. In the present illustrativeembodiment, the rotational speed of the asynchronous motor 6 can rangebetween 4000-10000 r.p.m. Preferably, a rotational speed in the range8000-10000 r.p.m. is utilized. In the present case, the rotation speedis about 9000 r.p.m. The rotational speed RPM' of the weaving machinecan lie within the range 500-1200 r.p.m.

The asynchronous motor 6 is electrically powered from an electricitynetwork 12 of a known known type. Preferably, the public electricalmains are utilized. The invention can function for different frequenciesof the electricity network. In Sweden, for example, the frequency is 50Hz. The invention also functions however at 60 Hz, for example. Theasynchronous motor 6 is connected to the electrical power supply networkvia a motor control 13, which is arranged to procure an increasedfrequency for the asynchronous motor. The motor control can increase thefrequency, for example, by 100-500%. The increase depends upon the motortype and the number of poles on the asynchronous motor. The frequency onthe network side is symbolized by 14 and at the output of the motorcontrol, which output is connected to the asynchronous motor 6, by 15.The motor control can also comprise or be connected to avoltage-compensating electronic circuit 16. The electronic circuit isarranged to ensure that the nominal voltage of the asynchronous motor ismaintained irrespective of the voltage U of the electrical power supplynetwork. The motor control can thus be connected to input voltageswithin a relatively large range, e.g. an input voltage range between200-575 volts. This means that the number of motor types for theasynchronous motor 6 can be substantially reduced.

In the figure, a conventional asynchronous motor is indicated by 6'. Theconventional asynchronous motor can be connected in a conventionalmanner to the drive shaft 5 of the weaving machine via an apparatus,which downwardly adjusts the rotational speed, similar to the apparatus8 according to the above. The asynchronous motor 6', having therotational speed RPM', has been shown to indicate a comparative case inrelation to the asynchronous motor 6. According to the invention, theasynchronous motor 6 shall be substantially oversped in relation to theconventional case involving the asynchronous motor 6'. The overspeedingfunction offers the advantage, among other things, that a substantialweight reduction can be achieved in relation to the case involving theasynchronous motor 6'. This weight reduction can be up to 50% or more.The conventional asynchronous motor 6' is assumed to be 2-polar, whichmeans that its connection to the 50 Hz frequency of the electricalnetwork 12 produces a rotational speed of about 2800 r.p.m. for themotor 6'. If this case is compared with the case in which theasynchronous motor 6 is 2-polar and operates at a frequency 15 of 130 Hzfrom the motor control, the rotational speed of the asynchronous motor 6becomes about 9000 r.p.m.

In FIG. 1, two conventionally arranged fly-wheels for smoothing peaks oftorque in the system have been shown by 17, 18. These flywheels areplaced on the low-speed side of the system and are relatively large interms of dimension and weight. These flywheels and the applications ofthe flywheels in the system are attributable to the conventional designof the asynchronous motor 6'. According to the invention, the flywheelfunction shall be arranged on the high-speed side of the drive systemand in this case the flywheels have been indicated by 19 and 20respectively. The application enables substantial reductions to be madein dimensions and weight in the last-named case. Thus, for example, thereduction in weight of the flywheels 19, 20 can be 75% of the weight ofthe flywheels 17, 18.

According to the inventive concept, the invention can be utilized inweaving machines comprising a computer control 21, which can be of aknown type and therefore does not need to be here described in greaterdetail. The computer control comprises, for example, a keyboard assemblyor actuating member 22 and an indicator panel 23. Into the computerapparatus can be programmed information on yarn type, yarn character,pattern, etc. Likewise, statistical data on the rotational speed of theweaving machine, e.g. the optimal rotational speed for a respective yarncharacter, can be programmed-in and stored. The motor control can also,in one embodiment, adapt the motor voltage to the asynchronous motor 6irrespective of dynamic variations on the network with regard tofrequency and voltage within specified variation ranges. The frequencyadaptation can also be carried out in dependence upon signals i1 fromthe computer control 21. By means of the signals and controls, thefrequency increase produced by the motor control 13 is thus able to becontrolled, preferably with simultaneous voltage control according tothe above, so that the frequency increase is related to the optimalweaving machine speed applicable to the yarn 4 in question, given aconstant speed-reducing function. In FIG. 1, the supply current to themotor control is indicated by i2 and the output supply current from themotor control to the asynchronous motor 6 by i3. The nominal voltage tothe asynchronous motor is indicated by U1. The signals i4 represent theinput current to the asynchronous motor 6' in the said conventionalcase. In one embodiment, the adaptive setting of the rotational speedfunctions as follows: the computer of the weaving machine works out theoptimal production speed, using the fault statistics of the weavingmachine as input data. Speed information is transmitted to the motorcontrol as a desired target value. If the cumulative stopping time ofthe machine is herein calculated to be excessive, the motor rotation ofthe asynchronous motor is reduced. Consequently, consideration canherein be given first to the yarn quality and second to the manning ofthe plant. The system as such becomes self-adjusting and the speed canbe adapted according to operating stops/the number of faults, storagetimes, etc.

In the figure there is also shown a coupling 24 disposed between theflywheels 17, 18 and the drive shaft of the weaving machine.

By virtue of the above, a speed control is therefore integrated,procured by means of a frequency increase in the motor control 13. In acase, for example, in which the drive system is of the order ofmagnitude of 4.5 kW, a 1.5 kW 2-pole asynchronous motor can be utilized,which is therefore fundamentally envisioned for a rotation of 2800r.p.m. 1.5 kW asynchronous motor is designed as a high-speed motor withbetter/good stator lamination quality, which yields the 4.5 kW at 9000r.p.m. The belt drive is also adapted in accordance herewith and, by wayof example, a so-called "Poly-Velt" belt drive can be utilized. Theabove offers a series of advantages. The efficiency is substantiallyimproved as outlined below. No extra apparatus is required for inchingand reversed motional direction. Large savings are achieved in terms ofweight and costs. A 2-pole 4.5 kW asynchronous motor weighs about 28 kg.A 2-pole 1.5 kW asynchronous motor weighs about 13 kg and producesequivalent torque on the low-speed side by means of speed-reducingapparatus. A price reduction of about 40% can obtain for theasynchronous motor and the reductions can likewise be achieved by theuse of fly-wheels. The motor control can be frequency-controlled and anoptimized production speed can be set on the control panel of theweaving machine, see 21 above. Similar motors can be utilized for 50/60Hz. A smaller number of motor types can be utilized, as can a smallernumber of transformer sockets, in order to safeguard running withinlarge variations in the supply voltage. The motor control can carry outcompensations for various input voltages or supply voltages. An adaptivesystem which automatically adjusts to the optimal production speed canbe arranged. Stable motor speeds can be achieved thanks to the motorcontrol and the variations, in the embodiment of the invention, are only1/3 of those in the case in which standard motors are used. Theelectronic motor control can be designed with a soft start-up and softstoppage of the asynchronous motor, which should be compared with thestandard case which very often produces high starting currents. Betteradaptation to the first pick of the machine can be achieved. By runningthe motor at overspeed before activating the coupling, it is possible toeliminate the slow first pick. This function too reduces the size of theflywheel or flywheels.

According to the invention the asynchronous motor is designed to operatewith substantial overspeeding, with better lamination quality in thestator in relation to the standard case. In addition, it is possible toexchange the shaft and bearing for a shaft and bearing of smaller size,e.g. a size which is one number smaller. The cooling operation can alsobe realized and can be made, for example, to form part of the beltdrive. A high-drive belt is also utilized. The weaving machine and drivesystem can operate with a closed feedback loop and speed control whichproduces a 1-3% higher production speed. With a 2-pole asynchronousmotor of the standard type for 4.5 kW, a loss is generated in the systemat a maximum load of about 0.9 kW. This figure can in fact be improved,by some percent, thereby resulting in a higher price for the motor assuch. A 4.5 kW motor with 84% efficiency can be improved to 86%efficiency at an additional cost of 10%. For the same additional costpercentage, a 1.5 kW motor can be improved from 79% to 85%, since in thecase of small motors the production costs can be given priority over theefficiency rating. A 2-pole a synchronous motor of the high-speed typeand 1.5 kW produces an efficiency of about 85% at maximum load and 2850r.p.m. The losses at maximum load and 2850 r.p.m. are only-about 0.26kW. The losses at maximum load and 8900 r.p.m. are about 0.27 kW.Compensations for variations in the supply voltage can herein beutilized. Better quality in the stator laminations provide compensationsfor high stator frequency. The loss of power in the motor control can becalculated at about 0.14 kW. An efficiency-increasing effect can thus beachieved by the invention which, in the present case, produces savingsof about 0.4 kW.

As a result of the invention, 14 types of motor for 14 differentvoltages or 14 different transformer arrangements can be reduced to 5types of motor and 5 transformer arrangements respectively within thevoltage range 200-575 volts. The respective motor control can bearranged for 200-240 volts with ±10%; 260-346 volts with ±10% variation;380-415 volts with ±10% variation; 440-480 volts with ±10% variation;and 550-575 volts with ±10% variation. By virtue of this division into 5ranges, a technically simply constructed and cost-effective solution tothe motor control can be achieved. In a system according to the above,there is a need to be able to store a kinetic energy of the order ofmagnitude of 3500 joules. The belt drive in the high-speed system yieldsat least 2800 joules. By enlarging the width of the belt pulleys, it iseasy to achieve the necessary kinetic energy.

A motor control which meets the above-stated requirements shall bedescribed, by way of example, with reference, among other things, toFIG. 2. In the present case, the motor control is 3-phase and isarranged for the voltage 340-456 volts and the frequency range 45-65 Hz.The output to the motor yields 4.5 kW at 8900 r.p.m. The ambienttemperature is assumed to be 0°-50° C. and the working life of thedevice about 30000 running hours. The control comprises protectionagainst over-temperature and has a voltage restriction incorporatingupper voltage protection and lower voltage protection.

FIG. 2 shows a combined frequency-conversion and voltage-adaptation unithaving components which are known. The motor control can be connected toa 3-phase network, e.g. to the public electricity mains network 26, viaa rectifier unit 27, filtering unit 28 with filter and choke and abridge unit 29 having, for example, six power transistors. By means ofthe components 27-29, the line frequency 14' is converted to the supplyfrequency 15' to the three-phase asynchronous motor 30. The bridge unitchops the direct-current voltage which is obtained from the units 27 and28 and provides the motor with varying frequency. The voltage U₁ to themotor is adjusted with a voltage-adaptation unit 16' using so-called"PWM-technology" (of known type). A micro-computer (-controller) feedsinput voltage and supply current via an AC/DC converter 32 anddetermines the correct lead times to the PWM-unit 16, which lead timesare transmitted via a line (lines). The information i_(v) on desiredrotation speed and hence also frequency is acquired from the computer ofthe weaving machine, preferably in serial form. The rotational speed ofthe motor 30 is represented by a signal i_(m), which is supplied to themicrocomputer 31. The latter communicates also with the weaving machinevia an adaptation unit 33. The said signal i_(v) represents a targetvalue which is acquired from the weaving machine, the computer of whichworks out the speed target value in dependence upon fault statistics andany other input data. The actual value i_(m) of the motor 30 is fed backto the microcomputer. The latter also realizes information i_(s1) andi_(s2) to the computer of the weaving machine.

The weaving machine speed can thus be optimized at any moment or duringany work stages.

The invention is not limited to the above embodiment shown by way ofexample but can be modified according to the following patent claims.

I claim:
 1. A drive apparatus for driving a weaving machine at aspecific rotational speed, said weaving machine having a drive shaft,said drive apparatus being relatively light in weight as compared to aconventional weaving machine drive apparatus, said drive apparatuscomprising:a motor control unit connected to an asynchronous motor andto an electric supply network, said motor control unit including a meansfor converting a frequency of said electrical supply network to asubstantially higher frequency and supplying said motor with said higherfrequency for operation at a higher rotational speed (r.p.m.); and aspeed reducing unit connected between said motor and said drive shaft ofsaid weaving machine, said speed reducing unit reduces the rotationalspeed (r.p.m.) of said motor whereby said motor drives said weavingmachine via said drive shaft at the rotational speed (r.p.m.) of saidweaving machine.
 2. The apparatus according to claim 1 wherein saidmotor is approximately 50% of the weight of a conventional motor for aweaving machine which operates at the frequency of said electricalsupply network.
 3. The apparatus according to claim 1 further comprisinga means for controlling said motor control unit to provide predeterminedfrequencies to said motor.
 4. The apparatus according to claim 1 whereinsaid motor control unit further comprises:a rectifier connected to saidelectric supply network, said rectifier providing a rectified signal; afilter connected to said rectifier, which filters the rectified signal;a bridge unit connected to said filter which chops the rectified signaland supplies said higher frequency to said motor.
 5. An apparatus toincrease the efficiency of a weaving system comprising:at least oneweaving machine driven by at least one asynchronous motor; a means forincreasing frequency connected to a power supply network and to said atleast one motor, said means for increasing frequency providing afrequency substantially higher than a frequency of said power supplynetwork to said at least one motor, whereby said motor is oversped; andan electronic compensation member connected to said motor whichstabilizes a voltage input of the motor.
 6. The apparatus according toclaim 5 wherein said means for increasing frequency comprises:a firstmember which measures the input voltage; and second members which,dependent upon said input voltage, supply said motor with a nominalvoltage in a pre-determined range.
 7. The apparatus according to claim 4wherein said means for increasing frequency over speeds said motorwithin a range of 100-500% of its nominal rotational speed.
 8. A driveapparatus for a weaving machine, having a drive shaft, and beingrelatively light in weight as compared to a conventional weaving machinedrive apparatus, said drive apparatus comprising:an asynchronous motor,and means for operating said motor at an oversped state, said motoradapted to actuate the drive shaft of said weaving machine via aspeed-reducing unit; and at least one flywheel connected to a high speedside of the drive system for storing a substantial part of the generatedkinetic energy.
 9. The apparatus according to claim 8 wherein saidflywheel is directly connected to an output shaft of said motor, saidoutput shaft having a high r.p.m.
 10. A drive apparatus for driving aweaving machine at a specific rotational speed, said weaving machinehaving a drive shaft, said:a motor control unit connected to anasynchronous motor and to an electric supply network, said motor controlunit including a means for converting a frequency of said electricalsupply network to a substantially higher frequency and supplying saidmotor with said higher frequency for operation at a higher rotationalspeed (r.p.m.); and a speed reducing unit connected between said motorand said drive shaft of said weaving machine, said speed reducing unitreducing the rotational speed (r.p.m.) of said motor such that saidmotor drives said weaving machine via said drive shaft substantially atthe rotational speed (r.p.m.) of said weaving machine; and a computerapparatus which predicts optimal weaving speeds for a specific yarncharacteristic, said computer apparatus communicating with said motorcontrol unit to control the higher frequency such that the weavingmachine operates at an optimal speed.
 11. The apparatus according toclaim 10 further comprising:a rectifier connected to said electricsupply network, said rectifier providing a rectified signal; a filterconnected to said rectifier, which filters the rectified signal; abridge unit connected to said filter which chops the rectified signaland supplies said higher frequency to said motor.
 12. The apparatusaccording to claim 10 wherein said motor control unit comprises amicrocomputer which detects a rectified line voltage and controls avoltage determining unit which determines the voltage supplied to saidmotor; andwherein an actual rotational speed of said weaving machine iscommunicated to said microcomputer and compared with said optimalweaving speed, whereby said microcomputer adjusts said actual rotationalweaving speed.